1. Field of Invention
The present invention relates to an electronic tag and a signal modulation method thereof. More particularly, the present invention relates to an active electronic tag and a signal modulation method thereof.
2. Description of Related Art
With the advance of radio frequency technology, an electronic tag with a radio circuit has been used widely in, for example, identity identification, door entrance security system or electronic money.
Conventionally, an electronic tag works passively, which is driven by a detecting signal and a carrier transmitted from a reader, and the electronic tag utilizes the coupling effect of antennas to affect the amplitude of the carrier on the reader by varying its load resistance.
However, while most of electronic products are becoming increasingly thinner, lighter and miniaturized, electronic tags are still limited by the sizes of their antennas and cannot be miniaturized. The reason is that the information transmission distance is limited by the antenna dimension of the electronic tag. When the antenna dimension of the electronic tag is decreased, the coupling coefficient between the antenna of the passive electronic tag and the antenna of the reader is also decreased, and thus the change of the load resistance on the passive electronic tag is unable to or only minimally affect the voltage on the reader. As a result, the information stored in the passive electronic tag cannot be transmitted to the reader effectively.
Therefore, in order to simultaneously shrink the electronic tag and maintain the information transmission efficiency of the electronic tag for facilitating various applications of the electronic tag, there is an urgent need to solve the problem mentioned above.